1. Field of the Invention
The present invention is related to design of adjustable lenses, and especially to a design of a lens comprising a gel or elastomer disposed on bendable glass, wherein a piezo electric element is arranged in contact with the glass providing a bending of the glass when voltage is applied on the piezo electric element providing adjustment of lens parameters.
2. Description of the Related Art
There is an increasing demand for low cost, high volume solutions for adjustable lens elements in an ever increasing number of applications. The popular use of cameras in mobile phones represents an amount of millions of lenses. The design of such lenses requires fulfillment of a plurality of requirements, such as ease of operation when fitting the lens on top of a camera module in the mobile phone, providing as few operational steps as possible, etc. These challenges are even greater when the lens arrangement comprises tuneable parameters, such as encountered in auto focus lenses, wherein the focal length must be adjusted to fit the distance from the lens to the object to be photographed, for example. Such lenses are usually complex designs comprising movable parts, for example, which can make it difficult to assemble the lens in a reasonable manner. A further challenge with such designs are the ever increasing requirement to provide as thin lens assemblies as possible. Thin and lightweight mobile phones and cameras is a must in the marketplace.
Usually, it is necessary to have a stack of lenses atop an image sensor (a CMOS or CCD sensor), in order to focus light from the object to be photographed down to the sensor. A schematic illustration of a lens stack is illustrated in FIG. 1. By proper design of the total lens stack, the focus lens (rectangular in the schematic) can be located either closest to the photographing object or in between other lens elements. The role of the focus lens element is to shift focal point continuously from infinity to a minimum focal distance, which is determined by the application of the camera, for example. Focal distances may be in the range of 5-50 cm, for example.
In prior art there are some examples of compact adjustable lens designs. For example, in the article “Design, fabrication and testing of a micro machines integrated tuneable micro lens”, by Weisong et. Al., Journal of Micromechanics and Microengineering, 9 May, 2006, disclose a lens assembly wherein a liquid in a cavity may be compressed or elongated to achieve an adjustment of focal length of the lens. However, mass production comprising filling liquid may be a difficult and time consuming task.
JP 02-178602 disclose a lens assembly wherein a couple of transparent base materials with a liquid in between provides a bending of the base materials by applying a voltage on piezo electric elements disposed on one of the base materials, wherein the bending provides a desired curvature of the surfaces of the lens assembly.
JP 2000-249813 disclose a lens assembly comprising a deformable transparent material disposed in between two bendable transparent plates. A common actuator can bend the plates to provide a shift of the focal length of the lens assembly.
JP 01-140118 disclose an adjustable lens assembly comprising a piezo electric polymer with transparent electrodes on top of a cylinder container comprising a transparent liquid. Voltages applied onto the piezo electric polymer provides a curvature of the polymer, and hence a shift of focal length.
Therefore there is a need for a lens design providing simple adjustment of the lens, wherein the lens assembly is easy and cheap to mass produce.